The present invention relates generally to microwave and millimeter-wave devices such as antennas and cavities, and more particularly to microwave and millimeter-wave devices using chips including high-temperature superconducting films.
Conventional, low-temperature superconducting materials have been used to reduce ohmic losses in ultrahigh Q cavities at microwave frequencies. Low-temperature superconducting materials, however, possess a number of disadvantages. For example, significant constraints are placed on the operation of such devices due to the requirement to operate at liquid helium temperatures. Additionally, photons in the millimeter-wave/far infrared region may cause transitions across the superconducting energy gap, removing the superconducting properties. There may also be limitations caused by thermal excitations across that gap.
High-temperature superconducting (HTSC) materials have been discovered whose transition to the superconducting state occurs at temperatures above 25 Kelvin (K). These HTSC materials include rare earth elements such as yttrium, lanthanum, and europium combined with barium and copper oxides. An example of such a HTSC material is the Y-Ba-Cu-O system. See J.G. Bednorz et al, Z. Phys., B 64, 189 (1986); and M.K. Wu et al, Phys. Rev. Lett. 908 (1987). These materials have critical temperatures of up to approximately 90 K or above.
HTSC ceramics have been used in high frequency cavities and waveguides. See U.S. Pat. No. 4,918,049, the entire disclosure of which is hereby incorporated by reference. Additionally, granular ceramic HTSC materials have been used to make antennas and cavities. See "Superconductivity Starts to Go Commercial", Design News, May 8, 1989; S.K. Khamas et al., "A High-T.sub.c Superconducting Short Dipole Antenna", Electronics Letters, Vol. 24, No. 8, 460-461 (1988); Z. Wu et al., "Supercooled and Superconducting Small Loop Antenna", IEEE Colloquium on the Microwave Applications of High Temperature Superconductors, Oct. 24, 1989; T.S.M. MacLean al., "High Temperature Superconducting Antennas", British Electromagnetic Measurements Conference, National Physical Laboratory, Nov. 7-9, 1989; ICI Advanced Materials, "ICI Advanced Materials and AT&T Bell Laboratories High-Temperature Superconductive Resonator", Nov. 3, 1989; ICI Advanced Materials, "ICI Develops First Superconducting Dipole Antenna", Sep. 26, 1988; and C.E. Gough et al., "Critical Currents in a High-Tc Superconducting Short Dipole Antenna", ACS 1988, San Francisco, Calif.
The ceramic HTSC materials used in microwave devices having large areas and complex shapes are of low quality. That is, they have high surface losses. Thin (on the order of 0.50 microns) HTSC films have lower surface losses than ceramic HTSC materials. However, it is improbable that high quality HTSC films can be made for large and/or complex shapes because of the need to match lattice constants with those of the film substrate.
In view of the foregoing, an object of the present invention is to use HTSC thin film chips or discrete elements to make microwave and millimeter-wave devices of larger area and more complex shapes than otherwise possible.
Another object of the present invention is to make use of the low surface resistance of HTSC films in fabricating microwave and millimeter-wave devices.
Yet another object of the present invention is to use high-quality, low-loss HTSC films to cover metal surfaces that would otherwise be exposed to electromagnetic microwave or millimeter-wave fields.
Still another object of the present invention is to use small-area HTSC chips to provide high efficiency microwave and millimeter-wave devices having non-conventional shapes or large-area surfaces.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.